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- Albert, Andreas, et al.
(författare)
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Recommendations of the LHC Dark Matter Working Group : Comparing LHC searches for dark matter mediators in visible and invisible decay channels and calculations of the thermal relic density
- 2019
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Ingår i: Physics of the Dark Universe. - : Elsevier BV. - 2212-6864. ; 26
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Tidskriftsartikel (refereegranskat)abstract
- Weakly-coupled TeV-scale particles may mediate the interactions between normal matter and dark matter. If so, the LHC would produce dark matter through these mediators, leading to the familiar “mono-X” search signatures, but the mediators would also produce signals without missing momentum via the same vertices involved in their production. This document from the LHC Dark Matter Working Group suggests how to compare searches for these two types of signals in case of vector and axial-vector mediators, based on a workshop that took place on September 19/20, 2016 and subsequent discussions. These suggestions include how to extend the spin-1 mediated simplified models already in widespread use to include lepton couplings. This document also provides analytic calculations of the relic density in the simplified models and reports an issue that arose when ATLAS and CMS first began to use preliminary numerical calculations of the dark matter relic density in these models.
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| 5. |
- Fairbairn, Malcolm, et al.
(författare)
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Expansion history and f(R) modified gravity
- 2007
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :12, s. 005-
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Tidskriftsartikel (refereegranskat)abstract
- We attempt to fit cosmological data using f(R) modified Lagrangians containing inverse powers of the Ricci scalar varied with respect to the metric. While we can fit the supernova data well, we confirm the behaviour at medium to high redshifts reported elsewhere and argue that the easiest way to show that this class of models are inconsistent with the data is by considering the thickness of the last scattering surface. For the best fit parameters to the supernova data, the simplest 1/R model gives rise to a last scattering surface of thickness Δz~530, inconsistent with observations.
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| 6. |
- Fairbairn, Malcolm, et al.
(författare)
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Transparency of the Sun to gamma rays due to axionlike particles
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:20, s. 201801-
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that the Sun can become partially transparent to high energy photons in the presence of a pseudoscalar. In particular, if the axion interpretation of the PVLAS result were true, then up to 2% of GeV energy gamma rays might pass through the Sun, while an even stronger effect is expected for some axion parameters. We discuss the possibilities of observing this effect. Present data are limited to the observation of the solar occultation of 3C 279 by the Energetic Gamma-Ray Experiment Telescope in 1991; 98% C.L. detection of a nonzero flux of gamma rays passing through the Sun is not yet conclusive. Since the same occultation happens every October, future experiments, e.g., the Gamma-Ray Large Area Space Telescope, are expected to have better sensitivity.
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| 8. |
- Rydbeck, Sara, et al.
(författare)
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Testing the DGP Model with ESSENCE
- 2007
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :05, s. 003-
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Tidskriftsartikel (refereegranskat)abstract
- We use the recent supernova data set from the ESSENCE collaboration combined with data from the Supernova Legacy Survey and nearby supernovae to test the Dvali–Gabadadze–Porrati (DGP) brane world model and its generalizations. Combination of these data with a flatness prior and the position of the peak of the cosmic microwave background (CMB) radiation disfavours the DGP model slightly. Inclusion of the baryon acoustic peak from the Sloan Digital Sky Survey increase the tension of the DGP model with the data, although it is not clear how self-consistent this procedure would be without a re-analysis of the survey data in the framework of the DGP cosmology. Generalizations of the DGP model are tested and constraints on relevant parameters obtained.
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| 9. |
- Widmark, Axel, 1989-
(författare)
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Dark Matter in the Solar System, Galaxy, and Beyond
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is evidence that dark matter constitutes a majority of the Universe's matter content. Yet, we are ignorant about its nature. Understanding dark matter requires new physics, possibly in the form of a new species of fundamental particles. So far, the evidence supporting the existence of dark matter is purely gravitational, ranging from mass measurements on galactic scales, to cosmological probes such as the cosmic microwave background radiation. For many proposed models of particle dark matter, the strongest constraints to its properties do not come from particle collider or direct detection experiments on Earth, but from the vast laboratory of space. This thesis focuses on such extra-terrestrial probes, and discusses three different indirect signatures of dark matter.(1) A first part of this thesis is about the process of dark matter capture by the Sun, whereby dark matter annihilating in the Sun's core could give rise to an observable flux of high-energy neutrinos. In this work, I was the first to thoroughly test the common assumption that captured dark matter particles thermalise to the Sun's core temperature in negligible time. I found that the thermalisation process is short with respect to current age of the Sun, for most cases of interest. (2) A second part concerns a radio signal associated with the epoch when the first stars were born. A measurement of this signal indicated an unexpectedly low hydrogen gas temperature, which was speculated to be explained by cooling via dark matter interactions. In my work, I proposed an alternative and qualitatively different cooling mechanism via spin-dependent dark matter interactions. While bounds coming from stellar cooling excluded significant cooling for the simple model I considered, perhaps the same cooling mechanism is allowed in an alternative dark matter model. (3) Thirdly, a significant part of this thesis is about the mass distribution of the Galactic disk, which can be measured by analysing the dynamics of stars under the assumption of equilibrium. Although most of the matter in the Galactic disk is made up of stars and hydrogen gas, exact measurements can still constrain the amount of dark matter. Potentially, dark matter could form a dark disk that is co-planar with the stellar disk, arising either from the Galactic accretion of in-falling satellites or by a strongly self-interacting dark matter subcomponent. Together with my collaborators, I made significant progress in terms of the statistical modelling of stellar dynamics. I measured the matter density of the solar neighbourhood using Galactic disk stars and data from the Gaia mission. I found a surplus matter density close to the Galactic mid-plane, with respect to the observed baryonic and extrapolated dark matter halo densities. This result could be due to a dark disk structure, a misunderstood density of baryons, or due to systematics related to the data or equilibrium assumption. I also developed an alternative method for weighing the Galactic disk using stellar streams. This method does not rely on the same equilibrium assumption for stars in the Galactic disk, and will be used to provide a complementary mass measurement in future work.The different indirect probes of dark matter discussed in this thesis span a great range of spatial scales − from stellar interactions relevant to our own solar system, to the matter distribution of the Milky Way, and even cosmological signals from the dawn of the first stars. Through the macroscopic phenomenology of dark matter, the microscopic particle nature of dark matter can be constrained. Doing so is a window into new physics and a deeper understanding of the Universe we live in.
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